Potato Review

24 POTATO REVIEW JULY/AUGUST 2022 HAULM DESTRUCTION the order your fields are planted in.” Not all potato growers harvest in the same order they plant in. “Some of the growers I work with like to ensure they have good harvesting options in both wet and dry harvest conditions, but dividing their fields into ‘dry’ and ‘wet’ soil categories. This means that if the weather is dry, you can make a start on the ‘wet’ soils, and if it’s wet you can start on the ‘drier’ ones, thus widening your harvest window.” Evaluating when to start desiccation In-field variation of tuber development can make calculating the best time to desiccate challenging. When using a chemical desiccant, warm, dry weather is ideal for it to work quickly. “Where possible, haulm destruction needs to be done at the start of senescence as nutrients go down the haulm to the tuber so they continue to bulk. However, if you are growing a seed crop, you need to stop them earlier so they are not so big, but with the risk that the sudden stop will throw the plant into shock,” said Andrew. Andrew recommends doing a number of digs across different areas of the field to get a broad view of crop development and tuber size. Tubers should be cut open and inspected for any signs of vascular browning. “If you find any tubular browning you will know that it is likely to have been caused by crop stress, and not the shock of spray or flailing. It might be a good idea to let your customer know so that they are aware of the problem.” There are a number of different strategies which can be taken, including applying a desiccant spray to the haulm before flailing, or going in straight with a flail and then finishing off with a spray, or two or three applications of desiccants followed by a flail on the front of the harvester. “If you have a seed crop, the kindest thing is to spray the foliage to slow the crop down and make an artificial start to senescence, rather than flailing a green crop that is still growing vigorously.” If the desiccation plan is to first apply Spotlight (Carfentrazone-ethyl), Gozai (Pyraflufen-ethyl) or Albis (Pyraflufen-ethyl), water rates need to be at least 300l, emphasises Andrew. “Any less than that, the efficacy drops off, and it is better to go above this.” Both flat fan and forward-back nozzles work well, he adds, highlighting that getting the forward speed right is critical. Nevertheless, weather can mean make or break, and haulm destruction is never as good in cloudy, damp conditions as it is on a sunny day. “If possible, spraying should be done between mid-morning and late afternoon on a sunny day. If the weather is poor, you either have to accept that you will have poorer control or wait for better conditions.” He adds that since the withdrawal of diquat and the extra time now needed to ensure the crop is completely dead, some growers have preferred to bring their harvesting dates forward. While this increases their possibility of desiccating in better weather, if maleic hydrazide has been used, an interval of three to five weeks needs to be adhered to, he warns. If holding back for better weather is not an option, he advises that flailing is better than spraying. “Once the haulm has been topped, “Sometimes two stem desiccations are necessary, so you need to check your maximum applications for the product you use.” A well desiccated crop.